I'm pretty sure there is a config file that can be modded to speed up growth but I'm not sure which one it would be.

Also the single player or local hosted version of the game may have a slightly faster growth rate to begin with as it's not running all the time the growth would likely have been modified with this in mind

In My opinion the growth rates of plants make sense when you play on a Server thats online 24/7.

I mean most of the day you sleep or work anyway so its cool. Still the growth of trees is pretty slow.

For my Single Player game right now I manage to get through everything using /eat. Since the "server" is offline when I am not playing. I have to play 19 hours non stop for my tomatoes to grow. In the mean time I have basically eaten everything that occurs in the wild.

Instead of editing every plant manually to make it somewhat playable It would be cool to have (at least for single player) a function for a Plant-Growth Multiplier.. The Multiplier for Skill-Points on SP seems to be 24. So why not using the same for plants... I mean apart from the obvious reason that things Like trees would overgrow the whole planet in no time.

I think waiting 6 hours for a tree is somewhat reasonable on Singleplayer. For tomatoes, corn and what not it should not be longer than 1 to 2 hours.

Even tho the bug that was recently fixed that plants grow instantly on server start was helping very well on SP: Every hour when food supply was low I just relogged and was able to harvest everything again. That was pretty cool.

You can speed up your world Chat >> /openserverui >> Simulation >> Config >> TimeMult.
Just take your time end explore the server ui as you may find some other tweaks appropriate for your single player world.